The Times-Picayune archiveFederal investigators are close to completing their investigation into United Airlines Flight 497's emergency landing at Louis Armstrong International Airport.

Aviation investigations typically take 12 to 18 months, depending on the severity of the incident, Holloway said. He would not discuss a specific date for closing the case, nor speculate on the cause until the board's findings are made public.

The flight, which carried 109 passengers and crew members, left Armstrong International on April 4, 2011, at about 7:07 a.m. for San Francisco. But after ascending to about 4,000 feet, the pilots of the Airbus A320 received a smoke warning from the instrument panel.

Neither pilot smelled smoke, however, so they did not done masks, according to an NTSB interview two days later with captain Donley Moffer. Moffer told investigators he suspected smoke in a ventilation duct.

The pilots returned to Armstrong because the smoke warning, lighted in red, advised to "land ASAP," according to the interivew.

The flight landed at about 7:20 a.m. with no serious injuries even though the plane's nose wheel ran off the runway.